/* -*- Mode: C; c-basic-offset:4 ; -*- */
/*
 *  (C) 2001 by Argonne National Laboratory.
 *      See COPYRIGHT in top-level directory.
 */
#include "mpi.h"
#include <stdio.h>

#define MAX_PROCESSES 10

int main( int argc, char **argv )
{
    int              rank, size, i,j;
    int              table[MAX_PROCESSES][MAX_PROCESSES];
    int              errors=0;
    int              participants;
    int              displs[MAX_PROCESSES];
    int              recv_counts[MAX_PROCESSES];

    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );

    /* A maximum of MAX_PROCESSES processes can participate */
    if ( size > MAX_PROCESSES ) participants = MAX_PROCESSES;
    else              participants = size;
    /* while (MAX_PROCESSES % participants) participants--; */
    if (MAX_PROCESSES % participants) {
	fprintf( stderr, "Number of processors must divide %d\n",
		MAX_PROCESSES );
	MPI_Abort( MPI_COMM_WORLD, 1 );
	}
    if ( (rank < participants) ) {

      /* Determine what rows are my responsibility */
      int block_size = MAX_PROCESSES / participants;
      int begin_row  = rank * block_size;
      int end_row    = (rank+1) * block_size;
      int send_count = block_size * MAX_PROCESSES;
      
      /* Fill in the displacements and recv_counts */
      for (i=0; i<participants; i++) {
	displs[i]      = i * block_size * MAX_PROCESSES;
	recv_counts[i] = send_count;
      }

      /* Paint my rows my color */
      for (i=begin_row; i<end_row ;i++)
	for (j=0; j<MAX_PROCESSES; j++)
	  table[i][j] = rank + 10;
      
      /* Everybody gets the gathered data */
      MPI_Allgatherv(&table[begin_row][0], send_count, MPI_INT, 
		     &table[0][0], recv_counts, displs, 
		     MPI_INT, MPI_COMM_WORLD);

      /* Everybody should have the same table now.

	 The entries are:
	 Table[i][j] = (i/block_size) + 10;
       */
      for (i=0; i<MAX_PROCESSES;i++) 
	if ( (table[i][0] - table[i][MAX_PROCESSES-1] !=0) ) 
	  errors++;
      for (i=0; i<MAX_PROCESSES;i++) {
	  for (j=0; j<MAX_PROCESSES;j++) {
	      if (table[i][j] != (i/block_size) + 10) errors++;
	      }
	  }
      if (errors) {
	  /* Print out table if there are any errors */
	  for (i=0; i<MAX_PROCESSES;i++) {
	      printf("\n");
	      for (j=0; j<MAX_PROCESSES; j++)
		  printf("  %d",table[i][j]);
	      }
	  printf("\n");
	  }
    } 

    MPI_Finalize();
    if (errors)
        printf( "[%d] done with ERRORS(%d)!\n", rank, errors );
    else {
	if (rank == 0) 
	    printf(" No Errors\n");
    }
    return errors;
}
